ISM频段射频放大的小信号分析

为解决ISM频段小信号放大器降低失配与减小噪声之间的矛盾,提出了一种改善放大 器性能的分析方法,满足信源、晶体管与负载三者之间的失配程度在受限条件下增益和噪声 的最优化。指出增益、驻波比和噪声多个性能参数不能同时达到最优,提出了提高射频放大 器综合性能的方法。在24 GHz的ISM频段进行的仿真结果表明,驻波比越小,增益越 大,噪声系数受失配限制的影响,在满足增益的条件下失配受限会使噪声系数增大。     

噪声影响及计算变换图表

嗓声-温度的计算1.修正第二级噪声系数列线图在测量一个放大器的噪声系数时,往往需要在被测器件与衰减器之间插入附加增益.因此,测得的噪声系数是该级联的总噪声系数.当它的增益和第二级放大器的噪声系数已知值时,利用图1的列线图便可确定第一级放大器的噪声系数.     

基于ADS仿真的宽带低噪声放大器设计

设计了一个S频段宽带低噪声放大器.该放大器采用两级E-PHEMT晶体管(ATF541M4)级联结构,单电源供电模式.应用微波仿真软件ADS对匹配电路进行了优化设计,最后通过S参数及谐波平衡仿真得到放大器的各项性能参数,在2.7～3.1 GHz频率范围内噪声系数小于0.6 dB,带内增益大于30 dB,带内平坦度小于±1 dB,输入输出驻波比小于1.6 dB,1 dB增益压缩点输入功率不小于-15 dBm.仿真结果表明,该设计完全满足性能指标要求.     

快速设计参考图表

在测量一个放大器的噪声系数时,往往需要在被测器件与衰减器之间插入一放大级。因此,测得的噪声系数是两个放大器级联的总噪声系数。当第一级放大器的增益和第二级放大器的噪声系数为已知值时,利用图1的列线图便可确定第一级放大器的噪声系数。列线图的使用步骤1.将F_(1-2)(测得的总噪声系数) 和G_1(第一级的增益)相连并与a相交于一点;     

一种噪声系数低,功率匹配好的1.1千兆赫到2.4千兆赫的晶体管放大器

目前已制造了一种有潜力的低成本放大器微型组件。放大器是采用晶体管管芯和薄膜、梁式引线或片状元件等构成的混合微波集成电路。这种放大器的设计表明,已经有一种能够获得最低噪声系数的输入功率匹配技术。这种技术是使用反馈的方法实现功率匹配,而同时在晶体管的输入端保持最小噪声系数所要求的源阻抗。放大器采用Mullard公司生产的BFR90晶体管管芯,在无反馈时,放大器的失配电压驻波比大于3:1。在1.5千兆赫的中心频率,300兆赫的宽带范围内,对50欧姆的源,放大器的噪声系数已可做到3.5分贝,输入电压驻波比小于1.25:1。在1.1至2.4千兆赫的频率范围,两级匹配放大器的增益在16分贝与12分贝之间。     

一种低功耗K频段低噪声放大器

基于0.13 μm锗硅(SiGe)双极型互补金属氧化物(Bipolar Complementary Metal Oxide Semiconductor,BiCMOS)工艺，设计制作了一种高增益低功耗K频段低噪声放大器(Low Noise Amplifier,LNA)，通过优化晶体管尺寸及利用硅通孔设计高品质因数射极退化电感，降低了LNA噪声。实测结果表明，在1.6 V偏置条件下，该LNA在20 GHz的噪声系数等于1.94 dB，输入1 dB压缩点等于-29.6 dBm；18~21.3 GHz频率范围内，LNA增益大于23.3 dB，S11和S22均小于-10 dB。包含偏置电路功耗在内，芯片功耗仅21 mW，优于其他同等噪声系数的K频段SiGe BiCMOS LNA。该LNA可应用于卫星通信等K频段低功耗接收机系统。     

30GHz单片接收机

已经研制成功30GHz接收机用的几种单片集成电路.低噪声放大器芯片在14dB增益时噪声系数为7.dB,中频放大器在30dB控制范围内,增益为13dB.混频器和移相器变频损耗和插入损耗分别为10.5dB和1.6dB.     

7GHz频段单栅GaAs场效应管微波混频器

本文介绍了单栅G_aA_s MESFET微波混频器的工作原理和设计方法,给出了实际电路和测试结果.在6.7～7.2GHz频带内获得3.8±0.4dB转换增益,单边带噪声系数为7.2±0.3dB.     

20GHz低噪声高电子迁移率晶体管

日本东芝公司以减少卫星通信地面站接收机噪声系数为目的,研制出一种超低噪声高电子迁移率晶体管(HEMT),并用这种器件研制成20GHz低噪声放大器.对于卫星通信地面站装置,从价格和设置场所等考虑,要求天线小型化,为此应用目的,要求放大器低噪声化.作为超高频低噪声放大用的半导体器件,以前     

5cm低噪声场效应管放大器的设计

一、前言为解决提高整机接收灵敏度,降低噪声系数的要求,依据小型化、轻量化的原则,笔者在一块25×30mm~2,两块25×20mm~2的高铝瓷片上,利用一四一三研究所研制的低噪声场效应管做成两级C波段低噪声场效应管放大器。在5.1—6.1GHz频段上,获得噪声系数N_F:3～4 db(包括混频器等后级噪声系数在内);增益:G≥12db;1db增益压缩点为4 dbmw的结果。基本上得到了管子所给出的最好指标,达到了国内先进水平。分别在多部整机上试用,效果较好,一般可提高整机接收灵敏度10db左右。大大降低了接收通道对发射功率的要求,缓和了发送功率与接收间的矛盾。本文简要地分析介绍了场效应管放大器设计的基本思想及具体计算方法。     

改进高阶Vanderpol振子在微弱信号检测中的应用

在高精度的微弱光电信号检测系统中，存在信号被强噪声湮没的情况。针对这一问题，提出了一种基于改进高阶Vanderpol振子的微弱正弦信号定量检测方法。该方法利用改进高阶广义Vanderpol系统的高灵敏度与强抗噪性的特点提高了微弱信号检测的可靠性，再结合Lyapunov指数定量检测和90°移相补偿来实现混沌系统状态的量化判断和待测信号参数的高精度提取。仿真结果表明改进的Vanderpol振子比传统Vanderpol振子运算速度更快。与传统Duffing振子相比，在5%幅值检测误差范围内，改进的高阶广义Vanderpol系统可多获得37 dB的信噪比增益和60 dB的检测门限增益；与基于相轨迹突变定性检测待测信号幅相法相比，90°移相补偿幅相定量检测法在信噪比降低时其检测相对误差仍可控制在2%以内。改进算法实现了微弱正弦信号的高灵敏度和高精度的幅相检测。     

Retailers and apparel imports: variables associated with relative proportions of imports carried

Purposes of this exploratory study were: (i) to determine retailers' views toward imported apparel, (ii) to gain insight into retailers' reasons for carrying imported apparel, and (iii) to examine variables associated with relative proportions of imported apparel carried in stock. Interviewers surveyed 191 retailers in the eastern U.S.A., using a structured telephone interview. Data analysis included chi-square tests of association and frequency distributions. The proportion of stock retailers reported to be imported was cross-tabulated with a number of variables. Results gave insight into retailers' reasons for carrying imported apparel, although a majority appeared to favour domestic apparel; results also indicated some of the problems associated with carrying foreign-made goods. Results can be useful to manufacturers in their efforts to counter retailers' trend to carry increasing quantities of imported apparel and to educators preparing graduates for employment in this sensitive sector.     

Insiders' personal stock donations from the lens of stakeholder,stewardship and agency theories

This paper studies the relationship between personal stock donation by top executives and board of directors (insiders) of publicly traded corporations and their personal tax, shareholders' returns, and social responsibility. The study finds evidence that the timing of stock donations is driven by personal tax gain. The study further shows, comparing stock gift corporations relative to their non‐stock gift cohorts, that personal stock gifts are associated with lower short‐term and long‐term stock returns to shareholders. This implies that stock donation driven by insiders' personal gain adversely affects shareholder wealth. However, the likelihood and intensity of insiders to make personal stock donation is reduced when firms have strong corporate social responsibility (CSR). Agency theory explains insiders' opportunistic behavior, stakeholder theory is also supported by evidence that stock donation is negatively related to CSR, and stewardship theory offers a different view to explain the rationale behind insiders' stock donation and shareholders' reactions to stock gifts.     

GPS接收机射频模块

介绍了一种ＰＨ１５７５型ＧＰＳ接收机专用集成电路，它是一种双极性硅单片集成电路，具有集成度高、功耗低、相位噪声优良的优点，适用于要求成本低、集成度高、电池供电的便携式ＧＰＳ接收机。     

射频连接器振动对信号相位噪声的影响

振动环境作用于射频连接器会影响信号的相位噪声。为了提高通信质量,研究了振动对射频连接器相位噪声的影响。分析了振动条件下射频连接器对通过其中的高频信号产生相位噪声的基本原理,推导出了机械振动参数与其产生的相噪功率谱之间的数学关系,验证了振动对不同频率信号的影响关系,并在相应的试验中验证了推导结果的正确性。相关研究结果对分析射频连接器的工程应用中振动对信号的影响具有指导作用。     

Consumer complaint behaviour in the children's wear market in the U.S.

The purpose of this study is to gain a better understanding of consumer complaint behaviour in the children's wear market. Based upon an economic framework of complaint behaviour, the relationship between selected consumer and product characteristics and complaint behaviour for children's wear was examined by estimating separate logistic regression equations for private and public complaint actions. Variables found to be associated with complaint actions included the price of the item, income, level of dissatisfaction, garment type, family size and age of the youngest child. The results have specific implications for apparel marketers and provide an application of the complaint model to a product category that has not been investigated previously.     

矢量网络分析仪的时域功能在天线测量中的应用

介绍了利用矢量网络分析仪的时域功能测量天线系统驻波系数、增益和方向图的方法.这种方法通过确定各反射点的位置和反射大小,以及在天线增益和方向图的测量中去掉周围环境的反射影响,使测量的结果更精确.     

Asymmetric information and corporate derivatives use

We investigate the relationship between derivatives use and the extent of asymmetric information faced by the firm. Using alternative analyst forecast proxies for asymmetric information, we find evidence that both the use of derivatives and the extent of derivatives usage is associated with lower asymmetric information. Specifically, for firms using derivatives (notably currency derivatives) we find that analysts' earnings forecasts have significantly greater accuracy and lower dispersion. These findings support the conjectures of DeMarzo and Duffie (1995) and Breeden and Viswanathan (1998) who argue that hedging reduces noise related to exogenous factors and hence decreases the level of asymmetric information regarding a firm's earnings. © 2002 John Wiley & Sons, Inc. Jrl Fut Mark 22: 241–267, 2002     

Trainees' perceived knowledge gain unrelated to the training domain: the joint action of impression management and motives

Trainees' knowledge gains represent an important outcome in human resource development. In this research, we tested a model examining the joint influence of social desirability (impression management, self‐deception) and motives (need for power, need for approval) on trainees' self‐reported knowledge gain. We conducted a study with respondents who reported information related to individual differences and took a training program and reported their knowledge gain in domains that were both related and unrelated to the training program. Trainee unrelated knowledge gain was a function of the joint influence of individual predispositions (to impression manage or engage in self‐deception) and motives (need for power, approval). Our findings suggest that impression management and self‐deception are insufficient to influence respondents' reports of unrelated knowledge but do yield predictable patterns when examined with respondents' motives. We discuss these results and implications for human resource development research and practice.